The maneuverability of an articulated wheel loader is improved by adding rear wheel steering capability such that the loader can be steered by either articulation or by both articulation and rear wheel steering. One of the problems encountered with such vehicles is how to synchronize both types of steering in the dual steering mode. This is particularly troublesome on vehicles in which the hydraulic jacks associated with the articulation steering are much larger than the hydraulic jacks used for steering the rear wheels wherein the volume of fluid exhausted from the articulation steering jacks is drastically greater than the volume of fluid required to actuate the rear wheel steering jacks. It is desirable to synchronize the angle of the rear wheel steer with the articulation steer angle.
A solution to a similar problem is disclosed in U.S. Pat. No. 4,917,204 wherein both the front and rear wheels are steerable. Steering synchronization therein is achieved by using a diverter valve to divert the fluid exhausted from the steering jacks associated with the front wheels to power the steering jacks associated with the rear wheels in a master-slave relationship. Synchronization is easily achievable in that type of vehicle since the front and rear steering jacks disclosed therein are the same size. However, the simple employment of a diverter valve is not practical in a vehicle wherein one set of steering jacks are much larger than the other set of steering jacks.
The present invention is directed to overcoming one or more of the above problems.